1. Field of Invention
This invention pertains to the production and use of organic polymer frameworks and more particularly to the synthesis and use of transparent bulk conjugated polymers prepared from one or more liquid monomers containing at least one pi-electron conjugated moiety and at least one polymerizable moiety, through bulk polymerization.
2. Background
Scintillation is a phenomenon that has been exploited in some form to detect ionizing radiation for nearly a century. Exposure of certain materials to ionizing radiation such as x-rays, alpha and beta particles, gamma rays and neutrons results in the emission of photons from the material, typically in the visible, ultra-violet or infrared ranges. The light output of a scintillator material essentially depends on its efficiency in the conversion of the ionization energy to photons. The emitted photons from the scintillator material can be received by a photo-electric device such as a photomultiplier or charge coupled device where it is converted to an electrical signal. The resulting signal can be amplified, analyzed and recorded.
Early inorganic scintillation materials included CaWO4 and ZnS that were used in the study of x-rays and alpha particles respectively. The scintillation properties of a wide range of other materials were also investigated including activated halide crystals, lithium containing compounds, thallium activated NaI and core-valence luminescence of BaF2. Organic scintillators that emit light when exposed to different types of radiation have also been developed in recent years.
Medical imaging, geophysical exploration and other industrial applications contributed to the demand for more efficient high light output scintillators. Conventional plastic scintillators are typically composed of a polymeric matrix such as polyvinyltoluene (PVT) and a fluorescent compound such as diphenylstilbene (DPS). This material can be easily shaped and fabricated in various forms such as rods, sheets and cylinders. However, the typical polyvinyl or polystyrene based scintillators often need to be kept in a highly polished state and are susceptible to the formation of microcracks in the surface from use and are also sensitive to cleaning solvents such as alcohols.
Plastic scintillators have been shown to have comparatively higher absorption characteristics for electrons and neutrons but have a lower detection efficiency with gamma rays when compared with inorganic materials. The neutron detection efficiency is dependent on the energy, threshold, thickness and volume of the plastic scintillator used.
Only a small fraction of the kinetic energy of an ionized particle encountering a scintillator is lost in the conversion into fluorescent light, and the rest is dissipated in the form of heat or lattice vibrations. The radiation energy that is ultimately converted into fluorescence energy (scintillation efficiency) depends on the radiation particle type and its energy. Generally, the light output of a scintillator is different for different types of particles at the same energy. The light output ultimately determines the efficiency and resolution of the scintillator.
Scintillation efficiency is a function of the type of matrix, dimensions and fluor that are used. The absolute scintillation efficiency of a particular material is the ratio of the amount of energy of the emitted light to the energy lost by the ionizing radiation. A high absolute scintillation efficiency in a material is desired to maximize the detection sensitivity of the sensor to the ionizing radiation.
There have been many attempts to increase the scintillation efficiency of organic scintillators by exploring alternative polymer matrices. Such attempts have identified several polymers and monomers that exhibit increased efficiencies. However, plastic scintillators still only produce a quarter of the light output of inorganic materials and have been largely ignored in the field of gamma-ray measurements even though plastic scintillators are less expensive to manufacture, less temperature sensitive, rugged and machinable.
Accordingly, there is a need for increasing the efficiency and discrimination of organic scintillators in the detection of high-energy particles and ionizing radiation. There is also a need to economically produce a scintillation material that is stable, durable, optically transparent and machinable on a large scale. The present invention satisfies these needs as well as others and is generally an improvement over the art.